The present invention relates to an ignition system for an internal combustion engine and, more particularly, to an ignition timing control apparatus for an internal combustion engine of a vehicle which has a compact structure and is particularly effective for a two-stroke-cycle internal combustion engine, and which is also applicable to a vehicle having two wheels or four wheels and any other vehicle.
In an internal combustion engine, particularly two-stroke cycle internal combustion engine, an ignition timing satisfying an output requirement of the internal combustion engine with respect to an ignition timing control is ordinarily set. The ignition timing satisfying the output requirement is set, for example, as ignition timing IG/T in an advance angle with respect to a revolution number N.sub.e of the internal combustion engine as indicated by the solid line in FIG. 5.
However, during an operation at which a certain number of revolutions of the internal combustion engine is maintained (steady operation state), a restriction occurs due to irregular combustion or knocking. The steady operation has, with respect to the internal combustion engine revolutions N.sub.e, an ignition timing region, such as that represented by the hatched area A in FIG. 5, in which an irregular combustion occurs, and another ignition timing range, such as that represented by the hatched area B, in which a knocking occurs.
Accordingly, in the case of an ignition timing characteristic satisfying an output requirement, undesirable phenomena such as irregular combustion and/or knocking take place during the steady operation in an actual vehicle traveling. In addition, an irregular pulsation which occurs during steady traveling of a vehicle affects as a hindrance to make smooth the operation thereof.
Ordinarily, such undesirable phenomena as irregular combustion and knocking during the steady operation as described above can be improved or reduced by setting a lag of the ignition timing. In the conventional techniques, therefore:
(1) it has been practiced that the ignition timing is set with a lag in angle both during the steady operation and the accelerating operation such that a condition in a region represented by each of the hatched areas A and B in FIG. 5, in which the irregular combustion or knocking occurs, is avoided, and such that the output requirement is sacrificed; and PA1 (2) it is also known that a knocking detecting sensor is provided and a knock signal from the knocking detecting sensor is fed back to set a lag in angle of the ignition timing (see, for example, Japanese Patent Laid-Open Publication No. 180771/1983). PA1 a detection means connected to an internal combustion engine for detecting a revolution number of the internal combustion engine; and PA1 a control means operatively connected to the detection means for controlling an ignition timing period in accordance with the detected revolution number of the internal combustion engine, the control means being connected to an ignition unit connected to the internal combustion engine, PA1 the control means including an element for discriminating that the internal combustion engine is now in a steady operation state in a case where the detected engine revolution number is maintained by a predetermined time interval within a predetermined engine revolution number variation range and an element for setting, to the internal combustion engine, the ignition timing period for preventing irregular combustion and/or knocking when it is discriminated that the internal combustion engine is in the steady operation period and for setting, to the internal combustion engine, the ignition timing period satisfying an output requirement when it is discriminated that the internal combustion engine is out of the steady operation period.
In the above-described technique (1) entails a reduction in output (also in thermal efficiency) and is, therefore, not preferable. In particular, there is a problem of the output being reduced even during the acceleration requiring a certain output.
The above-described technique (2) realizes an improved system, but entails the problems of the construction being complicated and an increase in cost.
With respect to the ignition timing control for internal combustion engines, it has been also proposed that the ignition timing is controlled according to the intake air flow rate and the throttle opening for fuel supply of the engine as well as the revolution number of the internal combustion engine (Japanese Patent Laid-Open No. 279270/1987). However, this technique also entails problems of the system being complicated and an increase in cost.